Ventilation of Confined Spaces
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Transcript Ventilation of Confined Spaces
Ventilation of Confined Spaces
Confined Space Ventilation
Confined spaces are not normally designed
for convenient ventilation
Must take steps to:
• ensure air is breathable before entering
confined space
• maintain acceptable air quality in the confined
space during entry
Hotwork in Confined Spaces
Presents additional ventilation challenges
in confined spaces
Includes torch cutting, welding, brazing
and soldering, arch gouging
Hotwork in Confined Spaces
Remember… confined spaces concentrate
hazards!
Hotwork can create atmospheric hazards in
confined spaces from fumes, gasses and
vapors
Effective ventilation sometimes may only
be accomplished by mechanical
ventilation
Natural Ventilation in
Confined Spaces
“Chimney Effect”
• convection process created by temperature
changes
Occurs by sunlight heating vessel walls
and air within
If there is an opening in bottom and top of
vessel, upward draft created
Natural Ventilation Problems
Confined spaces rarely experience uniform
thermal conditions
Various sources of heat in confined spaces
• human bodies
• lighting
• hotwork processes
Natural Ventilation Problems
Factors such as sunlight, body heat,
lighting and hotwork are usually not
sufficient to move enough air to provide an
acceptable atmosphere
Overcoming Natural Ventilation
Problems
Must establish techniques and procedures
to provide adequate ventilation
It is easier to work with than against
natural convection.
Use of Mechanical Ventilation
Properly installed, can reduce or eliminate
respiratory protection requirements
Effective engineering controls usually less
dependent on worker attention than
respiratory protection
29 CFR 1910.134
When feasible, effective engineering
controls must be used rather than
respirators
When is ventilation necessary?
If atmosphere:
• contains insufficient oxygen or is oxygen rich
• contains flammable dusts or vapors
• contains hazardous or toxic vapors, mists,
fumes, gases, or fibers
When is ventilation necessary?
If atmosphere:
• is subject to activities that may generate
hazardous mists, vapors, fumes or gases, or
may create either an oxygen deficiency or
oxygen excess, and
• increases heat stress on workers to
unacceptable levels
CAUTIONS
Many people resist wearing PPE, including
respiratory protection
Tangle of supplied air hoses in vessel with
many welders can present a hazard
Ventilation- 29 CFR 1910.252(c)
Spaces that require ventilation
• work space less than 16 feet high
• volume less than 10,000 cubic feet per welder
• work areas with partitions, structural barriers,
or other barriers that significantly obstruct
airflow
Ventilation- 29 CFR 1910.252
Ventilation options:
• provide at least 2000 cfm of airflow for each
active welder; or
• provide each welder with a local exhaust
device
– local exhaust devices must be capable of
maintaining a velocity of 100 fpm toward the air
intake
Ventilation Requirements
29 CFR 1910.252 and 29 CFR 1926.353
require use of local exhaust ventilation or
supplied air respiratory protection when
performing hotwork using certain
substances
Ventilation Requirements
Fluorine compounds
Zinc
Lead
Cadmium
Mercury
Beryllium (local exhaust and supplied air
respirators are required)
Ventilation Requirements
Construction :
• chromium
• stainless steels (if using MIG processes)
Air Moving Devices
Two types:
• Fans
• Venturi-type eductors
Can be air, steam or electrically driven
Eductors
Sometimes called “air horns”
Air powered and rely on venturi effects to
move air
Criteria for Rating Air Movers
Free Air Delivery
Effective Blower Capacity
Quantity of air and air pressure required
(air-driven devices)
Electrical power requirements (electrically
driven devices)
Factors Reducing Performance
Equipment components in confined space
Maintenance/construction materials
erected in space
Obstructions in make-up air manway
Insufficient number of make-up air
manways
Factors Reducing Performance
More restrictions to overcome = less air
moved
Air moving into space equals amount of air
leaving the space
Air Driven DevicesPoor Performance
Reduced pressure and volume to air driven
devices from multiple users
Excessively long air hoses
Increasing Performance
Supplemental air compressors dedicated
to air mover use (air driven devices)
Supplemental air compressors connected
directly to plant air system
Eliminate “short-circuiting” of airflow
Designing Ventilation Systems
Configuration, contents and tasks
determine type of ventilation
• opening configuration
• properties of expected atmospheric hazards
• type of work being performed
Electrically Driven Centrifugal Fans
Designed to overcome higher static
pressures
Usually heavier than air-driven equipment
Can be used remotely to reduce noise
Due to power, can suck up debris
Local Exhaust
Single manway vessels
Interior obstructions that create “dead
spots”
Lack of feasible way to attach air-moving
device
Work with toxic metals
Local Exhaust
Effective only when it captures and
removes welding fumes and gasses at the
source as they are emitted
100 fpm capture velocity at the source of
fumes or gasses
Local Exhaust- Considerations
Long runs reduce airflow
Airflow loss minimized by use of smooth
ducting with large radius bends
Run flexible ducting as straight as possible
Consider using plenums for multiple
welders
Field test flow/personal air monitors
Make-up air quality
Mechanical ventilation uses surrounding
air
Make sure the make-up air is not a source
of airborne contaminants